Which halogens are gases at room temperature and pressure

Doing so gives them a full outer energy level, which is the most stable arrangement of electrons. Halogens often combine with alkali metals in group 1 of the periodic table. Alkali metals have just one valence electron, which they are equally "eager" to donate. Reactions involving halogens, especially halogens near the top of the group, may be explosive.

The halogen group is quite diverse. It includes elements that occur in three different states of matter at room temperature.

Fluorine and chlorine are gases, bromine is a liquid, and iodine and astatine are solids. Halogens also vary in color, as you can see in the figure below. Fluorine and chlorine are green, bromine is red, and iodine and astatine are nearly black.

Like other nonmetals, halogens cannot conduct electricity or heat. Compared with most other elements, halogens have relatively low melting and boiling points. Most halogens have a variety of important uses. A few are described in the table below. In hydrogen halides HX, where X is the halogen , the H-X bond gets longer as the halogen atoms get larger.

This means the shared electrons are further from the halogen nucleus, which increases the shielding of inner electrons. This means electronegativity decreases down the group. Halogens are highly reactive, and they can be harmful or lethal to biological organisms in sufficient quantities. This reactivity is due to high electronegativity and high effective nuclear charge.

Halogens can gain an electron by reacting with atoms of other elements. Fluorine is one of the most reactive elements. It reacts with otherwise inert materials such as glass, and it forms compounds with the heavier noble gases.

It is a corrosive and highly toxic gas. Fluorine can react with glass in the presence of small amounts of water to form silicon tetrafluoride SiF4. Thus fluorine must be handled with substances like the inert organofluorine compound Teflon.

Chlorine has maximum solubility of 7. Dissolved chlorine reacts to form hydrochloric acid HCl and hypochlorous acid HClO , a solution that can be used as a disinfectant or bleach:. Bromine has a solubility of 3. Iodine is minimally soluble in water, with a solubility of 0. Astatine is below iodine in Group 7. The colour of these elements gets darker as you go down the group.

Iodine is purple, and astatine is black. Predicting properties The halogens show trends in physical properties as you go down the group. Melting point and boiling point The halogens have low melting points and low boiling points.

Colour The halogens become darker as you go down the group.